The invention relates generally to electrical machines and more particularly to machine stators.
In the motor industry, it is commercially advantageous to have a motor be as small and cost-efficient as feasible. Conventional motor stators are fabricated by punching laminations with each having an outside diameter and semi-closed slots or insertion of stator windings. The laminations are stacked, annealed, and positioned in an automatic winding machine. Because of the small openings of the slots, the windings cannot be wound in a compact manner and typically occupy no more than about thirty-five percent of the slot area. Thus size reductions of conventional laminated motor stators are limited.
Commonly assigned Kliman et al., U.S. Pat. Nos. 5,680,692 and 5,793,138, describe winding insulated coils and then molding a magnetic-flux-carrying stator or rotor around the pre-wound coils. In molded embodiments, the core cannot be annealed to the same extent as a laminated yoke can be annealed due to limitations of the material and of the winding insulation. Thus, depending upon the size of the stator, the molding process has the potential to leave high stresses in the core. Additionally, magnetic powder is significantly more expensive than magnetic laminations.
Commonly assigned Kliman et al., U.S. Pat. No. 5,990,588, describes a plurality of circumferentially spaced ferromagnetic strips of various alternative shapes integrally formed in plastic material of a pump assembly enclosure for sealing the stator from fluid in the gap between the stator and rotor. The ferromagnetic strips are described as being in direct contact with respective pole teeth of the stator in a manner which did not noticeably degrade motor performance as compared with fully laminated stator embodiments. Windings are not shown or described.
Commonly assigned Erdman et al., European Patent No. 613,234 B1, describes winding coils (preferably of rectangular cross section) on a conventional high speed bobbin coil winding machine and inserting the wound coils on teeth without tips. In one embodiment of Erdman et al., laminated pole tips can be individually attached to each pole. Erdman et al. describes the individual attachment process as being time-consuming and expensive and provides an alternative embodiment wherein On annulus of alternating interlocking sections of molded extruded powdered iron/plastic composite and non-magnetic plastic sections is slipped into place and located with suitable keys using conventional positioning techniques. In several more specific embodiments of Erdman et al., the coils are wound to conform to the shape of the annulus and the coils are wound into trapezoidal shapes to maximize the use of the space between the stator teeth.
It would be desirable to have an motor fabrication process which more effectively balances the competing goals of low-cost and high-performance.